In recent years there has been growing interest in the use of semiconducting polymers for electronic applications. One particular area of importance is organic photovoltaics (OPV). Polymers have found use in OPVs as they allow devices to be manufactured by solution-processing techniques such as spin casting, dip coating or ink jet printing. Solution processing can be carried out cheaper and on a larger scale compared to the evaporative techniques used to make inorganic thin film devices. Currently, polymer based photovoltaic devices are achieving efficiencies up to 7%.
There is still a need for organic semiconducting (OSC) materials that are easy to synthesize, especially by methods suitable for mass production, show good structural organization and film-forming properties, exhibit good electronic properties, especially a high charge carrier mobility, good processability, especially a high solubility in organic solvents, and high stability in air. Especially for use in OPV cells, there is a need for OSC materials having a low bandgap, which enable improved light harvesting by the photoactive layer and can lead to higher cell efficiencies.
It was an aim of the present invention to provide compounds for use as organic semiconducting materials that do not have the drawbacks of prior art materials as described above, are easy to synthesize, especially by methods suitable for mass production, and do especially show good processability, high stability, good solubility in organic solvents, high charge carrier mobility, and a low bandgap. Another aim of the invention was to extend the pool of OSC materials available to the expert. Other aims of the present invention are immediately evident to the expert from the following detailed description.
The inventors of the present invention have found that these aims can be achieved by providing conjugated semiconducting polymers based on a 3,7-diaryl-benzo[1,2-b;4,5-b′]difuran-2,6-dione or 3,7-diaryl-benzo[1,2-b;4,5-b′]dipyrrole-2,6-dione core:
wherein X is O, S or N—R, R is e.g. H or alkyl, and Ar1 and Ar2 are aryl.
The monomers and polymers of the present invention are especially suitable for large scale production. At the same time, they show good processability, high solubility in organic solvents, low bandgap, high charge carrier mobility and high oxidative stability, and are promising materials for organic electronic OE devices, especially for OPV devices.
Derivatives of the benzodifuranone and benzodipyrrolidone have been used as red and purple dyes or pigments in U.S. Pat. No. 4,115,404 and Greenhalgh, C. W.; Carey, J. L.; Newton, D. F. Dyes and Pigments, 1980, 1, 103-120. Derivatives of the benzodithiophenone are described in Nakatsuka, M. et al., Chemistry Letters, 1983, 905-908. However, it has hitherto not been suggested to use such compounds as recurring units in semiconducting polymers.